1. Field of the Invention
The present invention relates to manufacturing microelectronics, and more particularly, to an apparatus for manufacturing a semiconductor device, a method for forming a polysilicon layer having hemispherical grains (HSG-polysilicon layer), and a method for forming a capacitor having the HSG-polysilicon layer as an electrode.
2. Description of the Related Art
To manufacture a highly reliable semiconductor device, it is important to set appropriate processing conditions. In particular, when the capacitance of a capacitor is increased by forming a hemispherical grain polysilicon (HSG-polysilicon) layer as a lower electrode to increase the surface area of the lower electrode, it is imperative to grow the HSG grains uniformly on an amorphous polysilicon layer.
To uniformly form HSG grains, a crystal growing process in which amorphous silicon accretes onto crystal silicon nuclei to form crystalline grains should be stable, e.g., temperature conditions in the process chamber should be steady. Also, the speed of silicon migration for forming the grains must be higher than the speed of amorphous silicon crystallization. Thus, to stabilize the crystal growing step and appropriately adjust the crystallizing speed, the amount of a source gas, the reaction time and temperature profile in the reaction chamber must be precisely controlled.
Unfortunately, the conventional technology for forming the HSG-polysilicon layer has not yet defined the optimal combination of the temperature profile in the reaction chamber, the flow rate of a silicon source gas, and the reaction (i.e., process) duration. One result is that the crystal growth step is easily disturbed by unsteady temperatures and non-optimal gas flow. Further, since the amorphous silicon crystallizing speed and the grain growing speed are not appropriately controlled, bald defects can be generated, in which HSG grains can grow abnormally as evidenced by higher reflectivity to light, and undesirable extraneous HSG grains may be formed on an insulating film beyond the region designed to form the lower electrode of a capacitor.
One problem leading to non-uniform HSG grains is caused by changes to the temperature profile in the processing chamber due to changes in the position of a wafer supporter. As the process proceeds, the wafer supporter moves from a position where loading and unloading occur and cooler ambient air is introduced into the chamber (a load/unload position), to a position where the crystal growing process occurs (a process position) and vice versa. In the HSG formation process, for example, the difference between temperatures at the load/unload position and the process position is over 70.degree. C. Therefore, when the loaded wafer and wafer supporter move from the load/unload position to the process position to form the HSG-polysilicon layer, the wafer, and wafer supporter, and chamber temperatures continue to increase slowly with time until the temperature difference is minimized. When subjected to such a constantly varying temperature, the HSG-polysilicon layer forming process becomes non-uniform.